1. Field of Invention
The present invention relates to conversion apparatus and more particularly to apparatus for emulating a plurality of different target systems.
2. Prior Art
In general, when older data processing systems are replaced by a new system having significantly different architectural characteristics, a substantial amount of the jobs that were programmed for executing by the old systems must also be executed on the new system. Various well known techniques have been used in assisting the new system in executing jobs. One such technique is that of translating each instruction from the machine language of the old system into the instruction format of the new or host system. An example of a system which employs the foregoing is disclosed in the co-pending patent application titled "Method and Apparatus for peripheral device assignment and Validity Check and Relocation, if Assignment is Valid" bearing Ser. No. 228,776 invented by James B. Geyer et al which is assigned to the assignee named herein. Other techniques include simulation and emulation. These are discussed in the articles titled "Emulation of Large Systems" by S. G. Tucker, "1401 Compatibility Feature on the IBM System/360 Model 30 by M. McCormack, T. Schansman, K. Womack and "The Spectra 70/45 Emulator for the RCA301" by R. I. Benjamin, all of which appear in the December, 1965 issue of the publication titled "Communications of the ACM". Additionally, an article titled "System 370" Integrated Emulation under OS and DOS" by Gary R. Allred published in Volume 38 of the AFIPS Conference Proceedings, 1971 discusses these techniques.
One of the most important functions performed by an emulator is that of executing efficiently the input/output (I/O) instructions of a target system. In general, prior art systems have taken rather specialized approaches in emulating the I/O functionality of target systems. The result is that such systems are unable to emulate target machine operations for a number of target systems having different I/O requirements. Therefore, the prior art systems in order to accommodate requirements of different systems require a considerable amount of software and increased overhead to perform those operations necessary to emulate the I/O structure of each such system.
Accordingly, it is a primary object of the present invention to provide a system for emulating the input/output structure of a plurality of different target systems.
It is a further object of the present invention to provide an emulator system which reduces the number of operations which are performed by the support software of the system.
It is a still further object to provide a system which can with a minimum of complexity and maximum speed efficiently emulate the requirements of a variety of different input/output systems.